Plural dipole vertical antenna with isolation chokes



Oct. 13, 1970 J. M. SEAVEY 3,534,371

PLURAL DIPOLE VERTICAL ANTENNA WITH ISOLATION CHOKES Filed July 10, 19683 Sheets-Sheet 1 FIG.I

INVENTOR.

JOHN M. SEAVEY BY Kmmim ATTORNEYS Oct. 13, 1910- PLURAL DIPOLE VERTICALANTENNA WITH ISOLATION CHOKES File'tl July 10, 1968 FIG. 5A

MI? I QLJBT J- M. SEAVEY 3 Sheets-Sheet 2 INVENTOR.

JOHN M. SEAVEY ATTORNEYS US. Cl. 343-722 9 Claims ABSTRACT OF THEDISCLOSURE A flexible multiple element linear array antenna usingferrite core chokes for control of mast currents and interelementisolation.

My invention relates to antenna construction, and particularly to anovel, flexible, multi-element linear array antenna.

Particularly for use in mobile, high gain UHF transmission andreception, an antenna which is flexible, light in weight and ofprecisely controllable radiation characteristics is highly desirable.Construction of suitable single radiator, single frequency antennas forthis purpose presents no problem in the present state of the art.However, where a multiple element array, in whichthe elements operateeither at the same or at different freqiiencies, is needed, conventionalconstructions tend to be complex, cumbersome, fragile and expensive. Itis the object of my invention to facilitate the construction offlexible, vertically polarized multi-element linear array antennas oflight weight and controllable radiation characteristics.

Briefly, the above and other objects of my invention are attained by anovel whip antenna construction in WhlCh the outer element is asupporting mast of non-con- ,Qducting, relatively flexible and yetstrong material, such as tubing of epoxy resin filled with glass fibers,or the like. Within this tubing are lodged the electrical components ofthe antenna of my invention. These elements comprise primarily one ormore relatively flexible coaxial cables, and a set of ferrite cores. Thecoaxial cable forms an upper or outer dipole comprising as one half theouter conducting sheathing of the coaxial cable, and as the other halfthe inner conductor of the coaxial cable, extending into the upper endof the mast. The inner conductor may either protrude linearly for theappropriate distance from the outer conductor to form the second elementof the dipole, or may be connected to any conventional radiator to servethe same purpose.

.In accordance with my invention, the outer dipole is mechanicallyconnected to, but electrically isolated from, a second dipole lower inthe mast. Isolation is attained by winding the coaxial cable one or moretimes about a ferrite core. The cable then runs down the mast to asecond ferrite core. It is also wound one or more times about the secondcore, and then runs down the mast to a third ferrite core. The cable iswound one or more times about the third core, and is then led to thereceiving or transmitting circuits.

So far as the inner feed circuit for the outer dipole is concerned, theferrite cores have no effect. However with respect to the sections ofconducting outer sheathing, the wound cores act as radio frequencychokes. Thus, the two sheathing sections, one extending from the uppercore to ice the center core, and the other extending from the center tothe lower core, act as the independent sections of a second dipole, oneof which may be excited with respect to the other by means to bedescribed. The result is a simple and effective arrangement by which twoindependent dipoles can be arranged in a thin and flexible insulatingmast and can be operated at the same or different frequencies withsubstantial electrical isolation between the two dipoles.

The manner in which the apparatus of my invention is constructed, andits mode of operation, will best be understood in the light of thefollowing detailed description, together with the accompanying drawings,of various practical embodiments.

In the drawings:

FIG. 1 is an elevational sketch showing the outer appearance of anantenna in accordance with my invention;

FIG. 2 is a schematic elevational view, with parts shown in crosssection and parts broken away, of an antenna in accordance with a firstembodiment of my invention;

FIG. 3 is a schematic plan view of a toroidal choke forming a part ofthe apparatus of FIG. 2, and also suitable for use in other embodimentsto be described;

FIG. 4 is a schematic plan of a cylindrical choke which, in certainembodiments, has size and fabrication advantages.

FIGS. 5A and 5B comprise schematic elevational views, with parts shownin cross section and parts broken away, of the top and bottom portions,respectively, of an antenna in accordance with a second embodiment of myinvention;

FIG. 6 is a schematic view, with parts shown in crosssection and partsbroken away, of a modification of the apparatus of FIG. 5B;

FIG. 7 is a composite graph of the isolation and reactancecharacteristics of the chokes of FIGS. 3 and 4; and

FIG. 8 is a graph illustrating the measured performance characteristicsof the antenna of FIGS. 5A and 5B under typical operating conditions.

FIG. 1 shows the typical external proportions of a completed antennaconstruction in accordance with my invention. Generally, the antennacomprises an outer flexible mast portion 1 of glass fiber filled epoxyresin or the like. A pair of coaxial cables, generally designated as 3and 5, protrude from the bottom of the mast 1. The lower portion of themast may be fitted with any suitable conventional mounting and connectorassembly, not shown, as will be apparent to those skilled in the artwithout further description.

It is apparent that it would be difficult, if not impossible, to showthe internal construction of the antenna while maintaining theproportions of FIG. 1. Accordingly, in FIGS. 2-4 of the drawings, thephysical proportions and locations of the parts have been somewhatdistorted in order to make the electrical aspects of the apparatusclear. More particularly, the lengths of the radiating elements arerelatively shorter with respect to the size of the cores than wouldnormally be the case in practice, and the diameter of the outer mast isshown considerably larger in proportion to its length than wouldnormally be necessary.

FIG. 2 shows the construction of one embodiment of the antenna of FIG. 1in more detail. The construction, and the relative proportions of theparts, may be more readily comprehended if it is mentioned that atypical dimension for the cables 3 and 5 is one-sixteenth of an inch inouter diameter. Of course, that dimension is merely illustrative and isnot in any sensecritical.

As shown in FIG. 2, there are located in the insulating rmast threespaced ferrite cores 7, 9 and 11. The cores 7 and 11 are spaced apartessentially a distance )\1/ 2, where M is a desired operatingwavelength. The core 9 is equally spaced from the cores 7 and 11.

The coaxial cables 3 and are each wound one or more times about the core7. When a cylindrical core is used, a standard bifilar winding geometryis employed. In practice, as a typical example, five turns would beappropriate for operation at 350 mHZ. For use with coaxial cables of thediameter mentioned above, toroidcores such as 7 could be ferrite toroids/2 inch in diameter and A inch The cable 3 extends upward to the core 9,about which it also is wound. The cable 3 then extends upwardly and isagain wound about the core 11.

From the core 11, the outer conducting sheathing 13 of the cable extendsupwardly a distance 1 /4, where 1 may be the same as, or different from,A The inner conductor of the cable protrudes upwardly from thetermination of the outer conductor 13 by a distance x /4.

The manner in which the cables such as 3 and 5 are wound on the cores ismore clearly shown in FIG. 3, illustrating the manner in which cable 3is wound on the core 11. As also shown in FIG. 3 a conventionaldielectric insulator 17 (part of the coaxial cable) separates theconductors 13 and 15.

FIG. 4 shows an alternate form of core 1111 that may be used toadvantage where the physical size of the apparatus, the number of turnsrequired by the operating frequency, or other considerations make itmore convenient. The forms of choke shown in FIGS. 3 and 4 have beenformed to have the same electrical characteristics, and either can beused in any of the apparatus herein described.

The second coaxial cable 5 is also wound on the core 7. Alternatively,it could be wound on a separate core in approximately the same location,if that construction proved more convenient. Above the core 7, the outerconductor 19 of the cable 5 extends along the cable 3 essentially to thecore 9, and in this region between the cores 7 and 9 the outerconductors 13 and 19 may be soldered together as suggested at 21. Theinner conductor 23 of the cable 5 is soldered to the outer conductor 13of the cable 3 above the choke formed by the winding on the core 9.

The chokes formed by the windings on the cores 7, 9 and 11 are notelectrically effective in the RF circuit including the conductors 13 and15. However, the choke 11 serves to electrically insulate the portion ofthe outer conductor 13 above it from the portion below it. The result isthat if, for example, the lead 15 is excited with respect to theconductor 13 at the bottom of the mast 1 with a voltage at thewavelength R the portion of the cable 3 above the choke 11 will radiateat 1 as a dipole electrically isolated from the lower portion of theantenna.

In a similar manner, the choke 9 serves to isolate the portion of theouter conductor 13 above it from the portion below it, so that when lead23 is excited with respect to the outer conductor 19 with a voltage atthe wavelength A a portion of the antenna between the chokes 7 and 11will radiate as a dipole at the wavelength The choke comprising the core7 serves both to resonate the lower dipole and to suppress mastcurrents.

FIGS. 5A and 5B show a double bay antenna, with double elements in eachbay, constructed in accordance with a modified embodiment of myinvention. As an aid in comparing the construction of FIGS. 5A and 5Bwith that of FIG. 2, basic corresponding elements have been givencorresponding reference numerals. Thus, the coaxial cable feeding theupper radiating elements has been designated 3, the cable feeding thelower elements has been designated 5, and the outer insulating mast isdesignated 1.

In the embodiment of FIG. 5A, the core 7 serves the same purposes as inthe construction of FIG. 1. The outer conductors 13a and 19a of thecables 3 and 5, respectively, are soldered together, as at 21, above thecore 7 to form the lower element of a first dipole of length x /2. Theconductor segments 13a and 19a are electrically isolated from portions13b and 19b, comprising the second element of the same dipole, bywindings of the cables 3 and 5 about a ferrite core 9, which performsthe same functions as the core 9 in FIG. 2.

The dipole element comprising the conductor sections 13b and 19b isterminated at the top by chokes formed by winding cable 3 about aferrite core 24a and winding cable 5 about a core 2412. These corescould comprise a single core, but are shown separately for clarity ofillustration.

The cable 5 is connected to the difference port of a conventional hybridjunction 25 connected as a difference T to divide power supplied to thedifference port between two collateral ports. One collateral port of thejunction 25 is connected to a coaxial cable 27. The cable 27 is firstisolated by winding it about a ferrite core, here shown as the core 24b.It is then laid down along the cables 13b and 19b and the outerconductor 29 of the cable 27 is soldered to the conductor portions 13band 19b. At the lower end, the inner conductor 31 of the cable 27 iselectrically connected to the outer conductor portions 13a and 19a belowthe core 9.

It will be apparent that by the construction so far described, a lowerdipole of length x /2 is formed that may be fed by exciting theconductor 23 with respect to the conductor 19. An upper dipole of length)i /2 is formed above the lower dipole to complete the lower bay in amanner next to be described.

A core 33 is positioned just above the hybrid T 25. The secondcollateral port of the junction 25 is connected to an extension of thecable 5. That extension is first isolated by winding about the core 33,and then passes up along an outer conducting portion of the cable 3. Theouter conductor 19c of the cable 5 is soldered to the outer conductor13c, and the extension 23a of the inner conductor 23 is connected to aportion 13d of the outer conductor of the cable 3.

Portions 13c and 13d are isolated from each other by winding the cable 3on a core 35. The upper portion 13d of the second dipole is terminatedby Winding the cable 3 on a core 37. That serves both to resonate thesecond dipole and to isolate the lower bay of the antenna, comprisingthe apparatus just described, from the upper bay, next to be described.

FIG. 5B shows the upper portion of the antenna, including the isolatingchoke 37 also shown in FIG. 5A. A lower dipole of the upper array isformed by sections 13c and 131 of the outer conductor of the cable 3isolated from each other by windings of the cable 3 0n a core 39. Theupper dipole element 13 is terminated by winding the cable 3 on a core41. The lengths of Be and 13] are each )i /4, where A may be the sameas, o r different from,

Above the core 41, the cable 3 is coupled to the difference port of asecond hybrid junction 43. One collateral port of the junction 43 isconnected to a coaxial cable segment 45. The cable segment 45 isisolated by winding about the core 41, and then extended along theconductor segment 13 The outer conductor of the cable 45 is soldered tothe conductor portion 13 The inner conductor 47 of the cable segment 45is electrically connected to the conductor segment 13e below the core39.

The second collateral port of the hybrid junction 43 is connected to theend of the cable 3, which is wound about the core 11 and arranged toproduce the terminal dipole exactly as described in connection with FIG.2. It will be apparent that the upper pair of dipoles may be excited atthe wavelength A by feeding at the bottom of the mast, using theconductors 13 and 15.

FIG. 6 shows a modification of the apparatus of FIG. 5B in which aconventional coaxial line T, rather than a.

hybrid junction, is employed. The T 44 is connected in the circuitirrthensame manner as the junction 43. However, since the voltages atthe terminals of the coaxial T are in phase, Whereas those at thecollateral points of the junction are 180 out of phase, a phasecorrection is needed. As shown in FIG. 6, the necessary phase correctionmay be made by including an additional cable segment 13b, of length M/Zbetween the T 44 and the core 11. Alternatively, if desired, the addedlength could be included in the cable 45 between the T 44 and the core41, rather than in the cable 13. The additional length, such as 13h, canbe packaged in the supporting mast 1 by folding it, or winding it into acoil. If desired, the-same ar rangement could also be used in place ofthe hybrid junction 25 in FIG. 5A.

FIG. 7 shows typical reactance and isolation characteristics obtainablewith A inch coaxial cable at 350 mHz., with Q2 ferrites /2 inch indiameter and inch in height, as a function of the number of turns of thecable about the core.

FIG. 8 shows typical performance characteristics of an array of the typeshown in FIGS. 5A and 5B. The performance characteristics are shown interms of the voltage standing Wave ratio (VSWR) as a function offrequency when the upper bay is used as a transmitter and the lower bayis used as a receiver.

The antenna construction of my invention can be extended to include anydesired number of dipoles of the same or different frequencies in thesame mast. As illusstrated in FIGS. 5A and 5B, where a cable such as Bis used to feed a dipole higher on the mast, any lower dipoles on themast are bypassed by soldering the outer conductor of the cable such as3 to the outer conductors of the lower cables such as 5 along each ofthe dipole elements to be bypassed. Thus, for example, a fifth dipoleoperating at a wavelength A, could be added below the lower dipole inFIG. 5A, using a third coaxial cable. The outer conductors 13 and 19would be soldered together and to the outer elements of that fifthdipole formed by the outer conductor of the third cable, below the core7. More complexlextensions of the same construction will be obvious tothose skilled in the art from the examples given.

While I have described my invention with respect to the details ofvarious embodiments thereof, many changes and variations will beapparent to those skilled in the art upon reading my description, andsuch can obviously be made without departing from the scope of myinvention.

Having thus described vmy invention, what I claim is:

1. In an antenna, a length of coaxial cable comprising an outerconductor and an inner conductor, first, second and third linearlyspaced ferromagnetic cores at intervals /4, said cable being wound atleast once about said first core, extending to and being wound at leastonce about said second core, extending to and between wound at leastonce about said third core, and protruding linearly from said third coreto a termination at a distance MM, and said inner conductor protrudingfrom said termination a distance A /4, whereby two electricallyindependent dipoles of lengths x /2 and x 2 are formed.

2. An antenna, comprising a flexible tubular non-conducting mast, threeferromagnetic cores mounted in linear spaced relation in said mast, afirst of said cores being located at least a distance from a first endof said mast, a second of said cores being located closer to said firstend than said first core and spaced from said first core about adistance x /4, said third. core being located closer to said first endthan said second core and spaced about k /4 from said second core, acoaxial cable comprising an inner conductor and an outer conductor, saidcable extending into said mast from a second end opposite said firstend, being Wound about said first core at least once, extending to andwound about said second core at least once, extending to and wound aboutsaid third core and protruding from said third core toward the end ofsaid mast, said outer conductor protruding a distance A /4 from saidthird core, and said inner conductor protruding a distance A /Z fromsaid third core, and means for exciting the portion of said outerconductor between said first and second cores with respect to theportion of said outer conductor between said second and third cores withan alternating voltage having a wavelength A 3. The apparatus of claim2, in which said last recited means comprises a second coaxial cableextending into said mast at said second end, being wound at least onceabout said first core, having an outer conductor extending along theouter conductor of said first recited cable between said first andsecond cores and being electrically connected thereto, and having aninner conductor extending through the outer conductor and beingelectrically connected to the outer conductor of said first recitedcable adjacent said second core and between said second and third cores.

4. In an antenna, a multiple element array comprising a length ofcoaxial cable having an inner and an outer conductor, first, second andthird ferromagnetic cores, said cable being wound at least once abouteach of said cores and comprising a first length extending between saidfirst core and said second core, a second equal length extending betweensaid second and said third cores, and a portion extending from saidthird core for a predetermined length, and an electrical extension ofsaid inner conductor equal to said predetermined length.

5. An antenna comprising a linear array of dipoles formed from a lengthof coaxial cable, in which a terminal dipole is formed by the outerconductor of said length of coaxial cable and by an electrical extensionof the same length of the inner conductor and at least one other dipoleis formed by equal adjacent lengths of the outer conductor of saidcable, and in which the several elements of the antenna formed byadjacent lengths of the outer conductor of the cable are electricallyisolated by portions of the cable Wound about ferrite cores.

6. The antenna of claim 5, in which said cable is of flexible material,the antenna comprising said cable and cores being mounted in a flexibletubular supporting mast of insulating material.

7. In an antenna, a two element bay comprising first, second, third andfourth linearly spaced ferromagnetic cores, said second core beingessentially a distance A /4 from said first core, said third core beingessentially a distance x /4 from said second core and essentially adistance M/Z from said first core, said fourth core being disposedadjacent said third core and beyond said third core in the directionfrom said first core toward said second core, a first coaxial cablehaving an inner conductor and an outer conductor, said first cable beingwound at least once about said first core, extending to and wound atleast once about said second core, and extending to and wound at leastonce about said third core, a second coaxial cable having an innerconductor and an outer conductor, said second cable being wound at leastonce about said fourth core and protruding linearly from said fourthcore in the direction from said first core toward said second core, theouter conductor of said second cable protruding a distance x /4 fromsaid fourth core, means comprising an electrical extension of the innerconductor protruding a distance A1/2 from said fourth core, a thirdcoaxial cable having an inner conductor and an outer conductor, saidthird cable being wound at least once about said third core, the outerconductor of said third cable extending along and being-conductivelyconnected to the outer conductor of said first cable between said secondand third cores, the inner conductor of said third cable being connectedto the outer conductor of said first cable adjacent said second core andbetween said first and second cores, and a power divider connecting saidfirst cable to said second and third cables between said third andReferences Cited fourth cores' UNITED STATES PATENTS 8. The apparatus ofclaim 7, in which said power di- 9 vider comprises? coaxial line T, andin which one of said 31391620 1/1964 Leldy et a1 343-7 2 second andthird cables includes a length )\1/2 between the 5 3,315,264 4/1967Brueckmann 343 791 power divider and the nearest end of its associateddipole.

9. The apparatus of claim 7, in which said power di- ELI LIEBERMANPnmary Exammer vider comprises a hybrid junction having a diiferenceport U S CL X R connected to said first cable, a first collateral portconnected to said second cable, and a second collateral port 10343-5787, 872 connected to said third cable.

